This invention relates to a magnetic drive mechanism for a pump having a flushing and cooling arrangement which allows for cooling and flushing of the magnetic surface of the rotary driven member.
It is common to use gear pumps with sealed magnetically coupled drives. Such magnetically coupled drives eliminate drive shaft seals, which are a major source of pump leakage and contamination of the environment. Generally, these types of pumps have a magnetic drive mechanism with a sealed housing separating the driving and driven members. A gap is provided between the driven member and the sealed cobtainer to allow for the circulation of cooling fluid to the rear portion of the rotary driven member and across the magnetic driven surface. Such a magnetically driven pump and drive mechanism is described in U.S. Pat. No. 5,165,868 issued Nov. 24, 1992.
Such magnetic drive mechanisms are sensitive to temperatures seen along the magnetic drive and driven surfaces. The magnets lose strength and efficiency as temperature increases. This problem is compounded because the magnets also lose strength as the distance between the inner and outer magnetic surfaces increases. Thus, it is common to keep the distance between the inner and outer magnetic surfaces to a minimum. However, keeping this distance to a minimum reduces the size of the gap between the fluid containment canister and the rotary driven member. Such a reduction in the width of the gap severely restricts circulation of the cooling fluid to the back side of the inner magnetic surface, thus resulting in increased temperature of the magnetic surface and decreased drive efficiency.
In addition, such magnetic drive mechanisms often use the fluid which is being pumped for circulation around the rotary driven member as the cooling fluid. In some instances the pumped fluid may contain harmful ingredients which have deleterious effects on the components of the magnetic drive mechanism when the pumped fluid is circulated through the magnetic drive mechanism resulting in premature wear and breakdown of the magnetic drive mechanism. In other instances the pumped fluid may contain contaminants, such that when the pumped fluid is circulated through the magnetic drive mechanism, the contaminants may build up in the cooling fluid passageways resulting in decreased circulation of the cooling fluid or the contaminants may completely block the cooling fluid passages. The contaminants from the pumped fluid may also build up on the magnetic surfaces of the drive mechanism causing damage and resulting in a loss of magnetic strength and a loss of drive efficiency.